The present invention relates to aircraft electrical systems and, more particularly, to electrical systems on aircraft that employ electric taxi systems.
In a typical aircraft employing an electric taxi system (ETS), landing gear wheels are driven by electric motors which are provided with electrical power produced by an on-board auxiliary power unit (APU). In order to fully realize the economic benefits of employing an ETS, main engines of an aircraft are not operated during ground-based movement. Consequently the APU is tasked with providing not only electrical power for the ETS motors but also air conditioning power and power for a full array of electrical loads of the aircraft. Thus an aircraft equipped with ETS may need to be fitted with a non-conventional high capacity APU.
Aircraft without ETS are pushed back from a gate with a tug. During tug push-back the tug controls the aircraft movement, including braking, so the crew do not use the brakes. It would be desirable to provide for push-back using ETS with a similar absence of need to use the brakes.
When the aircraft moves faster than the wheel actuator motors are being driven, the motors may become generators and push current back toward the power source. During ETS pushback, existing ETS may disengage wheels from drive motors with a wheel actuator clutch. Alternatively, regenerated power may be dissipated locally in power resistors. Frequent operation of the clutch is undesirable from a life and reliability perspective. Dissipating regenerated power into resistors is inefficient, generates heat which must be managed, and adds significant weight and volume to the system.
As can be seen, there is a need for an electrical system in which an ETS that may be powered with an APU having conventional output capacity. Additionally there is a need for such a system that accommodates regenerative braking and effectively utilizes electrical energy produced during such braking.